(a) Field of the Invention
The present invention is related to a method and system for controlling an exhaust gas flow in an engine system that safely maintains a temperature of a diesel particulate filter (DPF) or a diesel oxidation catalyst (DOC) in an over-run condition of an engine to uniformly maintain a purification rate of exhaust gas.
(b) Description of the Related Art
Generally, a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF), a nitrogen oxide purifying unit (LNT, lean NOx trap), and a selective catalytic reduction unit (SCR) have been considered in diesel engines of vehicle to cope with the exhaust gas regulations. The post processing system such as DOC, LNT, and SCR which are provided to reduce harmful material of exhaust gas are to be operated in a basic temperature area (e.g., without over heating) for chemical reaction.
Specifically, exhaust gas temperature is substantially low in a cold state of an engine (e.g., coolant temperature is less than 90 degrees Celsius), and excessive harmful material of exhaust gas is generated until the post processing device is activated. Accordingly, fuel is further used to increase the exhaust gas temperature to reduce the harmful material of the exhaust gas in a cold state of the engine. However, it may be possible to increase the exhaust gas temperature through fuel combustion, an intake air may be transferred to a post processing system without combustion in an over-run condition (e.g., coasting state, fuel unburned state), and therefore the post processing system may be cooled by the unburned intake air and the activation time of the post processing system may be delayed.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.